A cutting tool which uses a cutting insert including a circular-arc shaped cutting edge is widely used as it is suited for use in three-dimensional machining of shapes. A ball end mill and a radius end mill, etc., are known as this type of cutting tool. Further, a cutting tool which uses a cutting insert including a circular-arc shaped cutting edge can be used suitably for copy machining, etc., not only as a rotary cutting tool but also as a cutting tool for lathes. In a cutting tool which uses a cutting insert including a circular-arc shaped cutting edge, a peripheral side surface of the cutting insert comprises a cylindrical-shaped or truncated conical-shaped curved face which matches the shape of the cutting edge. Thus, when the curved face of the peripheral side surface of the cutting insert has a higher ratio than a flat face thereof, this is likely to lead to an unstable fixation of the cutting insert, and the cutting insert may be shifted in the rotating direction during cutting. Concerning a reception mechanism as to the rotating direction of a cutting insert, Patent Document 1 discloses a cutting tool. The cutting tool in Patent Document 1 is a cutting tool comprising a cutting insert and a tool body, wherein the tool body includes a leading end surface and an outer side surface leading to the leading end surface and extending from a leading end side to a base end side. The tool body comprises an insert mounting part for mounting a cutting insert on the tool body. The insert mounting part includes a base surface which comes into contact with a lower surface of the cutting insert and a side wall surface which comes into contact with a peripheral side surface of the cutting insert. This cutting tool includes a reception mechanism which receives a rotational moment which acts on the cutting insert such that the cutting insert mounted on the insert mounting part is rotated on the base surface. The reception mechanism includes an engagement part (first engagement part) formed in the lower surface of the cutting insert and an engagement part (second engagement part) formed in the base surface of the insert mounting part and is configured such that these engagement parts are engaged with each other. The second engagement part formed in the base surface corresponds to one specific portion of a surface which defines the first engagement part formed in the lower surface of the cutting insert. When, as viewed from a direction facing the base surface, the base surface is divided into two areas by a boundary (first virtual plane) which passes through the center of gravity of an upper surface of the cutting insert and which is parallel to the longitudinal direction of the cutting tool, the engagement part formed in the base surface is formed on the outer side surface side (opposite side to the side where the side wall surface is located) of the cutting tool. Further, when the base surface is divided into two areas by a boundary (i.e., a second virtual plane orthogonal to the first virtual plane) which passes through the center of gravity of the upper surface of the cutting insert and which is perpendicular to the longitudinal direction of the cutting tool, the engagement part formed in the base surface is formed so as to be located in an area on the base end side of the cutting tool.